Salt-rejecting continuous passive solar thermal desalination via convective flow and thin-film condensation

Passive solar desalination is an emerging low-cost technology for freshwater production. State-of-the-art desalinators typically evaporate water using wicking structures to achieve high solar-to-vapor efficiency. However, wicking structures have limited salt rejection capability, which typically limits the operating duration to several hours. In addition, few studies have demonstrated efficient condensation to achieve a high solar-to-water efficiency. Here, we report a passive inverted single-stage solar desalinator that achieves continuous desalination and efficient condensation by convection-mediated salt diffusion and a novel mode of thin-film condensation. We experimentally demonstrate a record-high continuous passive desalination and salt rejection test duration of 168 h (7 days) under one-sun illumination. Our desalinator achieves a water collection rate of 0.5 kg m−2 h−1, which corresponds to a 32.9% solar-to-water efficiency. Furthermore, we develop a theoretical transport model and perform a parametric study to guide further optimization. This work signifies an improvement in the robustness of current state-of-the-art desalinators.